In a conventional pixel circuit implemented in an active matrix/organic light emitting diode (AMOLED) display apparatus, a driving level VDD and a voltage threshold Vth of a driving transistor are latched simultaneously. However, the driving transistor functions as a diode in the pixel circuit during a latching period, which is equivalent to charge an extra large resistance and a capacitor via a source electrode of the driving transistor, so that the charging of the capacitor is very slow, and a predetermined voltage may not be reached by fully charging during a predetermined period, while merely a particular voltage less than the predetermined voltage may be reached by charging. The ratio of the particular voltage and the predetermined voltage is called as a charging ratio, and thus the latched driving level should be multiplied by the charging ratio. As a result, the driving level VDD may not be totally compensated during a light-emitting period.